some radiators cold

[nsilk]

hi i have a baxi bahama 100 that has been nothing but problems for years.the current problem is that 2 rads down stairs and 2 up stairs are very hot and the other 4 upstairs and 4 down stairs are cold or luke warm.so far i have bleed and flushed the system,manually checked diverter valve all ok.the only thing that appears strange is that when the boiler starts up to heat ch it appears to only stay on for a few seconds i haven't really checked the pump.what would be the best way to check for this(the pump is grundfoss type up 15-60 up).oh also the hot water seems to fluctuate in temp.any suggestions would be appreciated thanks

 

[corgiman]

try turning off the rads that work and see if that improves the cold rads

 

[bengasman]

turn power off at mains
unscrew big chrome screw on pump, should start dripping.
if so, set pump to 1, turn heating on and roomstat to max
turn power back on, if pump does not spin, replace
if pump spins, turn power off, close pump, set to 3 and turn power on

 

[corgiman]

Unlikely to be the pump ben as the bahama is soo ulikely to heat the upstairs rads via gravity

 

[bengasman]

Unlikely to be the pump ben as the bahama is soo ulikely to heat the upstairs rads via gravity

?

 

[corgiman]

you were asking him to check the pump, but he does have some rads that work, so IMHO its unlikly to be a faulty pump.

 

[nsilk]

yes if i turn off hot rads the cold ones get hotter.have also unsrewed plug on pump water comes out.the boiler also makes a loud brrrr noise then slowy fades(sorry about the sound effects) could there be a problem with the heat exchanger there are 2 on the boiler 1 above the burner and a plate heat exchanger near controls.thanks for all the input

 

[corgiman]

sorry I dont undersatnd what ayou are saying about the heat exchangers?

it sounds like you have a balancing problem, do a search and you will be fine

 

[nsilk]

sorry not balancing.what i was thinking about heat exchanger could it be restricting the flow so as to only supply to rads nearest boiler thermistostor sensing water at temp to early and switches supply off.im no plumber but i work on sterilising boilers(autoclaves) in laboritorys

 

[nsilk]

oh yes other problem that may be related to this is the same noise the boiler makes first thing in the morning when heating starts up and the only way to stop this noise is to run the hot water tap at the same time as supplying ch but this stops after 30 odd mins

 

[bengasman]

I was thinking along the lines of an almost dead pump, no movement on setting 1, a shiver on 2, and reluctant spinning on 3.

 

[nsilk]

after draining ch rads ect again totally stripping down boiler.i found black crusty stuff in a small filter inlet to ch pump.once cleaned out all work well for a while then same prob came back.so i fitted a gate valve then a y inline strainer and after 2 days of isolating this strainer and cleaning out the crap now seems totally clear and now everything works better than ever.thanks for all the advice

 

[JohnD]

black crusty stuff

X400 and a Magnaclean is what you need

I seem to have been saying that all day.